Solvent and Polymer Stereochemistry Play Key Roles in Deuterium Exchange and Partial Racemization of Polypropylenes

Abstract

Recent reports have described deuterium exchange reactions on polyolefins; such isotopic labeling enables powerful analytical techniques, but exchange on isotactic polypropylene was previously unsuccessful. Here, we report successful exchange reactions on isotactic and syndiotactic polypropylenes, revealing the key role that the polymer stereochemistry and reaction solvent play in the mechanism of adsorption and exchange. Alteration of the polymer stereochemistry accompanies exchange in some cases, though molecular weight is preserved in all reactions.

Tuning the phase behavior of semicrystalline hydrogenated polynorbornene via epimerization

“…Thus, a combination of different initiator systems (to tune m : r ) and different hydrogenation routes (to impart different levels of trans units) can effectively tune T cc , while maintaining high crystallinity (Δ H ) and T m . Moreover, the choices for hydrogenation route are not limited to those presented here; for example, a highly active Pt/Re hydrogenation catalyst has recently been shown to induce partial epimerization of polypropylene at 170 °C with a proper choice of solvent and may be similarly active during PN hydrogenation as well.…”

Isotope Effects on the Crystallization Kinetics of Selectively Deuterated Poly(ε‐Caprolactone)

“… T m showed a relationship of T m (D0) > T m (D6) > T m (D4) > T m (D10). Melting point and crystallization temperature depression of deuterated polymers has been reported in many studies . However, the T m of D4, lower than that of D6, does not follow this trend.…”

“…Deuterated polyethylene (PE) was proved to be the key in elucidating the shish‐kebab superstructures and chain alignment of PE under cold‐draw through small‐angle neutron scattering (SANS) . Concurrently, various methods for the synthesis of deuterated polymers have been reported, including polymerizing the deuterated monomers, saturating polydienes with deuterium gas (D 2 ), and introducing deuterium at elevated pressure and temperature over different heterogeneous catalysts in the presence of D 2 . However, D substitution techniques sometimes exhibit nonsubtle isotope effects, such as different crystallization kinetics, which implicates the usage of D labeling in rigorously controlled crystallization studies .…”

“…For instance, Tashiro and coworkers found that at the same supercooling temperature ( ΔT c ), H/D blends of isotactic polypropylene (iPP) with higher D content had a higher crystallization rate, whereas H/D polyoxymethylene (POM) blends showed an opposite trend . Habersberger et al reported that a partially deuterated syndiotactic polypropylene (sPP) with statistical H/D distribution displayed a 12.5 °C reduction in melting point, suggesting the possibility that partial deuterium substitution is more disruptive to the crystal structure than full substitution . Jakowski et al reported that the orders in the crystallinity of the poly(3‐hexylthiophene)s (P3HT) with different substitution is P3HT‐D0 > P3HT‐D13 (side‐chain dueteration) > P3HT‐D1 (main‐chain deuteration) > P3HT‐D14, the opposite trend (P3HT‐D13 > P3HT‐D1) demonstrated that the reduced crystallinity of main‐chain deuteration is not caused by the slower crystallization kinetics because of the increased mass of deuterated P3HTs .…”

Recent Advances in Separation-Based Techniques for Synthetic Polymer Characterization

“…HT-GPC was recently used to assist in the understanding of the polymerization mechanism, such as chain walking polymerization, to support synthesis and characterization of model linear low density polyethylene (LLDPE) polymers, , for understanding changes in MWD as a result of hydrogen–deuterium exchange reactions, comprehensive analysis of novel grafted polyethylenes using multidimensional fractionation methods, deformulation of commercial LLDPE materials, and structure performance correlations involving adhesion of waxes . With the great enhanced awareness of environmental sustainability, HT-GPC was recently used to characterize plastic waste in the ocean and plastic residues digested by marine animals. , …”